Results: Following the microcycle significant changes (p < 0.05) in RSA as well as in CMJ and MRJ performance could be observed, showing a decline (%Δ ± 90% confidence limits, ES = effect size; RSA: -3.8 ± 1.0, ES = -1.51; CMJ: 8.4 ± 2.9, ES = -1.35; MRJ: 17.4 ± 4.5, ES = -1.60) and a return to baseline level (RSA: 2.8 ± 2.6, ES = 0.53; CMJ: 4.1 ± 2.9, ES = 0.68; MRJ: 6.5 ± 4.5, ES = 0.63) after 72 h of recovery. Athletes also demonstrated significant changes (p < 0.05) in muscle contractile properties, CK, and DOMS following the training program and after the recovery period. In contrast, CRP and urea remained unchanged throughout the study. Further analysis revealed that the accuracy of markers for assessment of fatigue and recovery in comparison to RSA derived from a contingency table was insufficient. Multiple regression analysis also showed no correlations between changes in RSA and any of the markers.

Conclusions: Mean changes in measures of neuromuscular function, CK and DOMS are related to HIIT induced fatigue and subsequent recovery. However, low accuracy of a single or combined use of these markers requires the verification of their applicability on an individual basis.

Mentions:
No significant time x sex interaction (p = 0.566) but a significant main effect for time (p = 0.010) was found for RSA test performance. MV was significantly lower following the six-day training intervention (post1: 4.84 ± 0.56 m·s−1) than at baseline (pre: 5.02 ± 0.52 m·s−1) or after recovery (post2: 4.97 ± 0.56 m·s−1). The respective changes were -0.18 ± 0.13 m·s−1 (p = 0.001; effect size = -1.51) from pre to post1 and 0.12 ± 0.26 m·s−1 (p = 0.003; effect size = 0.53) from post1 to post2.Differentiated by sex, markers of fatigue and recovery are illustrated in Fig 2, Fig 3 and Fig 4. There were no significant time x sex interactions with respect to any of the determined markers. However, a significant main effect for time was found for CMJ, MRJ, and 20-m sprint performance, as well as for contraction time of the RF and BF, CK, CRP, and DOMS. For CMJ and MRJ performance, a significant decline and a return to baseline level after 72 h of recovery could be observed (Table 3). In addition, athletes demonstrated a significant increase in CK and DOMS following the training program and a significant decrease after the recovery period (Table 3). The HIIT-microcycle also induced a significant increase in 20-m sprint time and contraction time of the RF and BF at post1 compared to baseline values. However, these increases were not reversible between post1 and post2 (Table 3). Dm of the RF and BF, as well as CRP, and urea were not different at post1 and post2 compared to baseline values (Table 3).

Mentions:
No significant time x sex interaction (p = 0.566) but a significant main effect for time (p = 0.010) was found for RSA test performance. MV was significantly lower following the six-day training intervention (post1: 4.84 ± 0.56 m·s−1) than at baseline (pre: 5.02 ± 0.52 m·s−1) or after recovery (post2: 4.97 ± 0.56 m·s−1). The respective changes were -0.18 ± 0.13 m·s−1 (p = 0.001; effect size = -1.51) from pre to post1 and 0.12 ± 0.26 m·s−1 (p = 0.003; effect size = 0.53) from post1 to post2.Differentiated by sex, markers of fatigue and recovery are illustrated in Fig 2, Fig 3 and Fig 4. There were no significant time x sex interactions with respect to any of the determined markers. However, a significant main effect for time was found for CMJ, MRJ, and 20-m sprint performance, as well as for contraction time of the RF and BF, CK, CRP, and DOMS. For CMJ and MRJ performance, a significant decline and a return to baseline level after 72 h of recovery could be observed (Table 3). In addition, athletes demonstrated a significant increase in CK and DOMS following the training program and a significant decrease after the recovery period (Table 3). The HIIT-microcycle also induced a significant increase in 20-m sprint time and contraction time of the RF and BF at post1 compared to baseline values. However, these increases were not reversible between post1 and post2 (Table 3). Dm of the RF and BF, as well as CRP, and urea were not different at post1 and post2 compared to baseline values (Table 3).

Results: Following the microcycle significant changes (p < 0.05) in RSA as well as in CMJ and MRJ performance could be observed, showing a decline (%Δ ± 90% confidence limits, ES = effect size; RSA: -3.8 ± 1.0, ES = -1.51; CMJ: 8.4 ± 2.9, ES = -1.35; MRJ: 17.4 ± 4.5, ES = -1.60) and a return to baseline level (RSA: 2.8 ± 2.6, ES = 0.53; CMJ: 4.1 ± 2.9, ES = 0.68; MRJ: 6.5 ± 4.5, ES = 0.63) after 72 h of recovery. Athletes also demonstrated significant changes (p < 0.05) in muscle contractile properties, CK, and DOMS following the training program and after the recovery period. In contrast, CRP and urea remained unchanged throughout the study. Further analysis revealed that the accuracy of markers for assessment of fatigue and recovery in comparison to RSA derived from a contingency table was insufficient. Multiple regression analysis also showed no correlations between changes in RSA and any of the markers.

Conclusions: Mean changes in measures of neuromuscular function, CK and DOMS are related to HIIT induced fatigue and subsequent recovery. However, low accuracy of a single or combined use of these markers requires the verification of their applicability on an individual basis.